This study finds that doping tin mono-sulfide (SnS) with different concentrations of manganese (Mn) (0-30wt%) results in a competition for anion bonding between tin and manganese during the hot-injection synthesis of the nanoparticles, creating lattice structures with strained crystallites and hence favoring the formation of the metastable zinc blende phase that has the crystal structure of sphalerite, a zinc ore. A typical hot-inject process was used to synthesize the SnS nanoparticles using oleic acid and oleylamine as solvents to produce the tin (doped with manganese) and sulfur precursors, respectively. We obtained a purely zinc blende phase at 260 degrees C when the doping concentration of Mn was increased to 30% while the stable orthorhombic phase was synthesized without doping. Powder X-ray diffraction (PXRD), High Resolution Transmission Electron Microscopy (HR-TEM) and Selected Area Electron Diffraction (SAED) results confirm the presence of the zinc blende phase at 30% Mn doping concentration. Ultraviolet-Vis-Near Infrared (UV-Vis-NIR) spectra show absorption onset at 980 nm for the orthorhombic phase and 840 nm for the zinc blende phase, and this blue shift can be attributed to the change in crystal phase structure. Electron spectroscopy for chemical analysis (ESCA) data shows that Mn2+ is doped substitutionally in place of Sn2+, while the strong presence of Sn4+ is due to the low enthalpy during the formation of tin vacancies. Doped SnS thin films without any catalysts were spin-coated on fluorine doped tin oxide (FTO) substrates and used as a working electrode in a photoelectrochemical cell and show photocurrent densities up to 53.26 mu A/cm(2) at an applied potential of similar to 1 V. These narrow band gap and low cost nanocrystals can be used for applications in future solar cells and other optoelectronic devices. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.